In many types of completions there are frequently a series of packers to isolate zones of different lengths. Some of these intervals can be fairly short but in each case the fluid in the annular space between the packers is subject to thermal loads from activities in the wellbore such as production or injection and other thermal inputs such as formation temperature fluctuations. These temperature variations can expand the trapped fluid between packers and in extreme cases can adversely affect the packer function as an isolation device.
Systems have been developed to use a movable piston with an isolated chamber that is initially at atmospheric or other pressure and have the other side of the piston exposed to pressure in the confined annular space after a rupture disc breaks at a desired depth in the borehole. These systems were illustrated in a single zone between two packers or spanning adjacent zones for thermally induced pressure fluctuations. These systems are shown in U.S. Pat. No. 8,347,969. A design for a pressure compensation system involving a movable piston is also shown in U.S. Pat. No. 8,066,074 FIG. 2A.
While these systems were workable, they were also costly to build because of the large pressure differentials across the chamber walls made for fairly thick walls needed to prevent burst or collapse during normal operation. The present invention addresses the need for pressure compensation in a variety of simpler designs that operate on a different concept. That concept is to take advantage of the differing solubility of salts in water, for example, so that the volume decreases on increasing solubility on rising temperature and vice versa. The concept is applicable to designs with a floating piston as well as other embodiments where a flexible and impervious bladder is used or even an enclosure for the salt that is porous with openings small enough to retain the salt while allowing the water to migrate in or out with temperature variations to change the volume as the pressure compensation vehicle. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the detailed description of the preferred embodiments and the associated drawings while realizing that the full scope of the invention is to be found in the appended claims.